(PHP 5 >= 5.5.0, PHP 7, PECL >= 3.0.0a1)
UConverter::toUCallback — Default "to" callback function
$reason
   , string $source
   , string $codeUnits
   , int &$error
   ) : mixed
This function is currently not documented; only its argument list is available.
reason
source
codeUnits
error